Common slot machines randomly select and display an array of symbols on actual or virtual reels, then grant an award to a player based on the occurrence of winning symbol combinations across activated paylines. Common symbol displays include a 5 column/reel by 4 row (5×4) matrix, a 5×3 matrix, a 3×3 matrix, and a 3×1 matrix.
Slot machine manufacturers and casinos have created many different ways to encourage players to bet more, play longer, and play certain machines. Such ways frequently involve designing the game to contain special features. Since the present invention involves symbols being held in place over successive games, certain related prior art is discussed below.
U.S. Pat. No. 7,331,866 to Rodgers describes a special feature involving free games. In one embodiment described in the '866 patent, reels that display a wild symbol during the free games are automatically held until the wild symbol is used in a winning combination or until a certain number of free games are played, whichever is first to occur. Playing free games with such a feature reduces the casino's revenue. The player wants the wild symbol to be used in a winning combination with the minimum number of respins, since there is no advantage to the player in not immediately using the wild symbol in a winning combination, and the player does not want to reach the end of the free game round without taking advantage of the wild symbol.
U.S. Pat. No. 7,326,113 to Bennett holds a special bonus symbol in position for successive games and allows all the reels to spin each game, while the held bonus symbol essentially overlays a spinning reel. Bennett holds the bonus symbol throughout a series of free games and does not extinguish the bonus symbol when it is used in a winning combination during the free games. The Bennett feature is only practical when there are a limited number of free games, since the special symbol must eventually be extinguished. As in the '866 patent, free games reduce the casino's revenues.
What is needed is a “special symbol” retaining feature that encourages the player to play non-free games and provides high revenue to the casino.